Ultrasonic thickness gauge operation tips
Ultrasonic thickness gauge can be used to measure thickness based on ultrasonic pulse reflection principle. It can be widely used for all materials in which ultrasonic wave can be transmitted in it in a constant velocity. Quality ultrasonic thickness gauge can be highly accurate when used properly. However, there are some factors can affect its degree of accuracy .Below we have listed main factor that may be related to its accuracy:
(1) Surface roughness. If the work piece surface is too rough, the probe and work piece surface coupling effect will be bad, and reflection echoes will be low, or even cannot receive the echo signals. So for surface rusted work piece, and poor coupling effect in-service equipment, piping, etc. we can do treatment like gritting, polishing, rasping and other methods on their surface to reduce roughness .Meanwhile, we can also remove the oxides and paint Layer to assure good coupling effect between the probe and the tested piece by using the coupling agent.
(2) Curvature radius. If work piece curvature radius is too small especially when test small-diameter tubes. In such case, we can use special probe for small bore tubes.
(3)Tested surface is not parallel with the bottom side. Ultrasonic wave is scattered when reaching bottom boundaries. Probe cannot get bottom side signal.
(4)Casting or austenitic steel should use special low frequency coarse-grain probe.
(5)Probe contact surface is damaged. After long-term use, probe sensitivity will be decline. Rub the probe surface with sandpaper or change a new probe.
(6)There is sediment in tested piece (such as in pipeline) .If sediment and work piece acoustic impedance have little difference, thickness gauge displayed value will be pipe wall thickness and sediment thickness combined value.
(7) Temperature. We can choose special probes for high temperature measurement (200-300℃).
(8) Coupling agent. Coupling agent is used to prevent air between probe and tested work piece and help ultrasonic wave effectively transmitted into work piece and achieve measurement purpose. In order to get accurate result, we should select proper type coupling agent according to different application .And coupling agent should be used in appropriate amount and should be well-distributed. Usually ,we put coupling agent in test piece surface, while when test high temperature work piece ,we should put coupling agent on probe surface.
(9) Selected sound velocity is wrong.
(10) Influence of stress. Solid material stress condition have a certain influence on sound velocity.